1. Field of the Invention
The present invention relates to combination/circuit interrupter/overvoltage protection apparatus for protecting AC power lines, coaxial transmission lines and communication lines from overvoltage conditions without the use of a separate ground conductor.
2. Discussion of the Related Art
Today many homes and buildings use sensitive electronic equipment such as home entertainment centers with expensive audio/visual equipment, personal computers, modems, printers, copiers, facsimile machines and telephone answering machines. This sensitive electronic equipment is connected to the outside world by AC power lines, coaxial transmission lines (both cable TV, satellite dish antennas and broadband internet connections) and communication lines (telephone, facsimile and high speed data). Because the electronic equipment is expensive, there is a need to protect the equipment from voltage surges occurring on the AC power lines, the coaxial transmission lines and the communication lines.
To fill this need a number of companies have developed plug in secondary surge suppressors which are designed to plug into AC wall outlets which carry a separate ground conductor and which accept three prong AC power plugs. The electronic equipment, which also has three prong AC power plugs, is then plugged into the secondary surge suppressor. Some plug in secondary surge suppressors currently available also provide overvoltage protection for coaxial transmission lines and/or communication lines. See, for example, Cawley U.S. Pat. No. 4,438,477 issued Mar. 20, 1984, which discloses a plug in secondary surge suppressor which protects both AC power lines and communication lines from overvoltage conditions using the ground obtained from the AC outlet by means of a three prong AC power plug.
While newly-built homes and buildings have AC outlets which carry a separate ground wire and accept three prong AC power plugs, older homes and buildings have AC outlets which only accept two prong AC power plugs. Therefore, plug in secondary surge arrestors currently being marketed (which have three prong AC power plugs and use the ground from the AC outlet to provide overvoltage protection) cannot be used in older homes and buildings with AC outlets which only accept two prong AC power plugs. A need therefore exists for a plug in secondary surge suppressor which can be used with AC outlets which only accept two prong AC power plugs.
While many homes today have ground fault circuit interrupters (GFCIs), those devices are only found in areas where water or moisture is present. GFCIs are current sensing devices and are tripped when a current imbalance is detected, generaly for a substantial period of time (up to 25 milliseconds) compared to the time a voltage transient exists (tens of microseconds). GFCIs do not respond to overvoltage conditions and do not protect against overvoltage condidtions. Indeed, GFCIs may be damaged by overvoltage conditions.